Chemical analysis is very important for life sciences research, clinical diagnostics and a wide range of environmental and process monitoring. An important class of measurements are conducted on particles such as cells or beads. For most of these application it is desirable that the analysis tools and methods be accurate, fast, easy to use and low cost.
Flow cytometry can be used for analyzing particulate elements including cells and beads, including beads having attached thereto biological materials. Exemplary flow cytometry apparatus and methods are described in U.S. Pat. Nos. 5,747,349; 5,981,180; and 6,139,800, which are incorporated herein by reference. Flow cytometry has disadvantages. For example the particles to be analyzed need to positioned very steadily, and only one particle can be detected at a time. Thus particles need to move at a steady flow rate for accurate results, but also at very high rates for high sample throughput. To obtain accurate results under these conditions, flow cytometry utilizes sophisticated, high speed, expensive detection electronics, which results in a relatively large and expensive instrument.
Other techniques for analyzing particles are described in Brenner, S.; et al, “Gene Expression Analysis by Massively Parallel Signature Sequencing (MPSS) on Micro Bead Arrays” Nature Biotechnology (2000), 18, 630–634; and Kitamori, T.; et al, “Integration of an Immunosorbent Assay System: Analysis of Secretory Human Immunoglobulin A on Polystyrene Beads in a Microchip” Anal. Chem. (2000), 72, 1144–1147.
The techniques described in these publications suffer from one or more disadvantages, such as an inability to analyze more than a single particle at a time, uncontrolled positioning of particles making analysis difficult, overlapping of particles so that the one particle interferes with the analysis of another particular, the need for all particles to have substantially the same size, and low signal to noise ratios, thereby making analysis difficult.
Accordingly, there is a need for a system for processing particles that is rapid, accurate, low cost and capable of processing multiple particles simultaneously, and that does not require all the particles to be of the same size.